Differential production of nitric oxide by endotoxin-stimulated rat and mouse neutrophils

There is controversy regarding the evidence for the production of nitric oxide (NO) by neutrophils (PMNs). The present study investigates NO production, as assessed by the biosynthesis of the end products, nitrite and nitrate, in the pellets and supernatants of rat and mouse peripheral blood neutrophils obtained during endotoxemia and of peritoneal carrageenin-elicited PMNs stimulated in vitro with E. coli lipopolysaccharide (LPS). We also investigated the induction of NO synthase by rat and mouse peritoneal cells. The intraperitoneal (ip) administration of LPS to mice (10 mg/kg) and rats (5 mg/kg) significantly increased plasma nitrate concentration by six and 23-fold, respectively. In vivo pretreatment with L-NGmonomethyl arginine (L-NMMA) significantly inhibited this production. Compared to animals injected with PBS, the cell pellets of blood PMNs obtained from mice, but not rats, 2 or 6 h after LPS administration produced significant amounts of nitrite (14 +/- 3 and 18 +/- 2 nmol/mg protein, respectively). Little or no nitrite was found in the incubating medium. In contrast, 6 h after a carrageenin challenge (700 micrograms) peritoneal neutrophils obtained from rats, but not mice, released high concentrations of nitrite into the supernatant during a 24-h period of incubation (34 +/- 0.8 microM). The nitrite concentration of the pellet of these cells was negligible. In contrast to the lack of increase in the amount of nitrite released into the supernatants, the in vitro stimulation of rat PMNs with LPS (10 micrograms/ml) for 24 h did increase intracellular nitrite concentration (from 0.8 +/- 0.07 to 8 +/- 0.3 nmol/mg protein). In mouse PMNs, LPS treatment caused only a small release of nitrite into the incubation medium (14 +/- 1 microM). There was no significant change in nitrite concentration in the cell pellets. These data suggest that rat and mouse neutrophils differ in their ability to produce nitric oxide following stimulation with endotoxin.